4-Port trunking on 2824/2848 not full bandwidth

[Andreas Schier]

Hello all,

we make a trunk over four ports from a 2848 switch to a 5412 core. The connection are 4 fiber channel cables. We connected 4 computers to the 2848 with 1Gbit cards. The trunk protocol is LACP. A 10Gigabit Server is connected to the 5412 core. We using the tool netperf which generates 100% traffic. All 4 computer starts netperf (simultaneous)to the server. When all 4 trunks are enabled only 2 trunks have the full load (2Gbit). When i disable one trunk i got full load on all 3 trunks. That is very strange. With 4 trunks less speed as with 3 ????

Does have anyone an idea ?

Thank you very much
Andreas

[Michael_Breuer]

Hi Andreas,

the load balancing is based on Source / Dest address (if available IP address otherwise MAC address pair). Each flow will be assigned to one link of the trunk. If you are unlucky the first and the second flow will be assigned to the same interfaces according to the calculation of the switch. So it could be possible that 4 flows just using two links. If feasible you could try to change the IP address (at least the last bits of the IP) of one server and check if this will change.

Cheers,

Michael